1. Field of The Invention
The present invention relates to a device which enables microvascular injections and manipulations directly into delicate and otherwise inaccessible blood vessels such as the capillary beds of the eye, thus providing means for more effectively treating diseases of the eye such as glaucoma.
2. Background of the Invention
Glaucoma is an ophthalmic disease which is manifested in most patients by an increase in intraocular pressure (normally equal to 5-25 mm of Hg) sufficient to cause degeneration of the optic nerve and defects in the visual field. It is a major cause of preventable blindness, affecting 2% of the adult population. Clinically, it is characterized by a specific type of optic nerve damage which accompanies the pathological increase in intraocular pressure. Most instances of elevated intraocular pressure are due to increased resistance to aqueous humor outflow from the trabecular meshwork, a sieve-like ringed structure located at the juncture of the iris and cornea.
Conventional glaucoma therapy concentrates on lowering intraocular pressure, either through eye drops, laser treatments, or surgery, all of which have significant drawbacks. Eye drops have been prescribed (either alone or usually in combination) either to inhibit the secretion of aqueous humor by the ciliary processes ("beta-blockers") or to improve escape of aqueous humor from the eye (such as pilocarpine, the miotic). To be effective, however, these drugs need to be administered in highly concentrated dosages because of poor penetration of the drugs into the eye. The administration of these drugs in such highly concentrated dosages creates a strong potential for ocular and systemic side effects, since much of these drugs drain into the nose and are absorbed into the bloodstream through the nasal lining. This is particularly a problem when the drugs must be administered on a continuous basis over a patient's lifetime.
Laser treatment is often used as an alternative or in addition to drug treatment, but the results are variable and often transient. The best current surgical treatment involves creating a channel for the fluid to escape out of the eye, thereby lowering the intraocular pressure. Although effective in controlling the eye pressure, this surgery has significant potential for producing sight-threatening complications including infection and bleeding, especially immediately after surgery (when eye pressure suddenly and dramatically decreases).
Accordingly, there is a need for new therapeutic approaches to lower intraocular pressure, using agents to alter the function of the trabecular meshwork permanently or at least on a prolonged basis. An important step towards such a therapy would be direct delivery of the agent into the trabecular meshwork. This approach would eliminate the problems of ocular or systemic side effects which have been encountered heretofore with the chronic therapeutic use of eye drops given in highly concentrated dosages. In addition, the margin of safety of such a therapy would be greatly improved over surgery if the administered drug acted gradually to lower intraocular pressure.
Micropipettes have been used in diagnostic procedures.
U.S. Pat. No. 3,986,834 discloses a kit in which a micropipette may be included for transferring reagents undergoing analysis of blood urea.
U.S. Pat. No. 4,050,316 discloses the use of an aspirator with a micropipette.
U.S. Pat. No. 4,078,892 discloses the use of a micropipette in transforming plasma into a diazo reagent for the determination of bilirubin.
Frenkel et al., 1989, Vestn. Ofthalmol. 105: 27-29 disclose the optimal shape of microneedles for suturing solid biological tissues, and the use of such needles for ophthalmological surgery.
Hori et al., 1983, Gann 74: 122-127 disclose the use of micropipetted to partially occlude microvessels without disturbing microcirculation.